We have recently developed a combined PET and CT scanner which allows, for the first time, registered CT and PET images to be acquired sequentially in a single device, overcoming alignment problems due to internal organ movement, variations in scanner bed profile, and positing of the patient for the scan. The PET/CT combines a Siemens Somatom AR.SP spiral CT scanner with a rotating EVAT ART PET scanner. To date, the PET/CT scanner has been used to study over sixty cancer patients. The aims of this competitive continuation are to extend the development and validation of the CT-based attenuation correction and to implement a new acquisition and image reconstruction procedures involving continuous patient bed motion. In order to achieve good signal-to-noise (SNR) for imaging any region of the body, it is proposed to improve both the CT-based attenuation correction procedure and the uniformity of the noise structure in the PET emission scan. CT-based attenuation correction provides almost noiseless correction factors. However, a number of aspects have emerged in which CT-based attenuation correction could be significantly improved. These include accounting for the effects of respiratory motion, truncation of the CT field-of-view, beam hardening, and intravenous contrast agents. In addition, validation of the CT-based correction will be performed by comparing emission scans reconstructed with CT-based factors to emission images reconstructed with factors obtained from standard PET transmission scans. For this purpose, the PET/CT scanner is equipped with collimated cesium point sources operating in singles mode. Further improvement in SNR can also be achieved by implementing continuous bed motion acquisition for the PET emission scan. Such an approach obviates the need to acquire overlapping bed positions that lead to axially varying SNR and lower overall efficiency. A feature of continuous bed motion will be the use of list mode data acquisition, which also offers the possibility of directly correcting for patient movement during the scan. The proposed developments in methodology will further improve the image quality of PET/CT studies.